Chips and turnings of actinide metals, such as uranium metal, are generated during the machining of such materials. The chips and turnings are generally stored under oil as they can react vigorously upon contact with either air or water. Scraps of these metals represent both a radiological and hazardous waste problem.
One general process of disposal involves the use of concentrated aqueous oxidizing acids to initially dissolve such an active metal. The dissolution is an exothermic, redox-type reaction and releases large amounts of hydrogen gas as a by-product of the metal oxidation. Governmental sites will not generally use such a dissolution process, because of the danger from the flammable hydrogen gas. Instead, the actinide metal, e.g., uranium, is burned to form the metal oxide prior to subsequent processing. The burning avoids any redox reaction in subsequent dissolution of the metal oxide. After dissolution, the metal oxide is purified from any contaminants by conventional techniques such as ion exchange or solvent extraction. Unfortunately, this process suffers several disadvantages, e.g., high operator exposure, an excessive number of operations, and poor overall process efficiency.
Previously, oxidants such as hypochlorites have been used as an oxidizing additive in the dissolution of uranium ores, e.g., in the in-situ leaching of uranium ores from subterranean ore deposits. For example, U.S. Pat. No. 4,312,840 describes the use of an alkali metal or alkaline earth metal hypochlorite to oxidize the uranium in a subterranean deposit from a tetravalent state (U.sup.+4) to a hexavalent state (U.sup.+6) in an overall process using an aqueous lixiviant having a pH within the range of 7.5 to 10.0. In a similar manner, U.S. Pat. No. 4,185,872 describes the use of hypochlorite to oxidize the uranium from a tetravalent state (U.sup.+4) to a hexavalent state (U.sup.+6) in an overall process using an aqueous lixiviant having a pH of at least 7.5 and containing an alkali metal sulfate leaching agent.
Surprisingly, it has now been found that reaction of a hypochlorite such as sodium hypochlorite with an actinide metal yields an insoluble actinide oxide material thereby forming an essentially inert uranium-containing material that may be isolated for storage, disposal or recycle.
Accordingly, it is an object of this invention to provide a process of converting an actinide metal such as, e.g., thorium, uranium, or plutonium, into an insoluble actinide oxide material, without the need for initial burning and subsequent dissolution.
It is a further object of this invention to provide a process of converting an actinide metal such as, e.g., thorium, uranium, or plutonium, to an insoluble actinide oxide material, at low temperatures, i.e., preferably such conversion occurring at or near room temperature.
It is yet another object of this invention to provide a convenient low temperature synthesis of an actinide oxide material from an actinide metal such as thorium, uranium, or plutonium.
It is still another object of this invention to provide a convenient low temperature synthesis of an actinide oxide nitrate material, e.g., uranyl nitrate (UO.sub.2 (NO.sub.3).sub.2), from an actinide metal such as thorium, uranium, or plutonium.